[EricH]

Originally Posted by GeeTwo

No, I understood, though perhaps I took your strategy even farther than you meant. Here's what I'm thinking as "making a stack":

• Drop two totes through the chute. The first lands on the floor, the second on top of the first.
• Lift those two totes high enough for the next step (about 30-36") (2 totes lifted)
• Drop two more totes through the chute.
• Lower the raised stack onto the stack on the floor, and continue to the low end of the stroke.
• Lift the four totes high enough for the next step (4 totes lifted).
• Drop two more totes through the chute.
• Lower the raised stack onto the stack on the floor, and continue down at least far enough to disengage from any totes.
• Open the release gate for the main robot to score it.

Six totes per stack when doing pairs is 2 for the first lift and 4 for the second lift; 2 + 4 = 6. Fifteen totes on single-stacking is 1 + 2 + 3 + 4 + 5. It doesn't matter where the lift engages the tote; the amount of lift must be as high as the bottom of the tote moves up plus the "engagement distance", that is the amount of motion between the bottom of the stroke and the tote being lifted off the floor. I'm estimating that to clear a 2-stack with a few inches for free entry of the second tote would be about 30-36".

That second bullet is where you missed him. The floor-level tote stays there to act as a catcher/ramp until the stack is complete.